MOS type elements have been widely used in solid-state image pickup devices for some time. Within a solid-state image pickup device, a plurality of pixels that generate a signal potential based on a received light intensity are provided, the plurality of pixels making use of common output lines to transmit the signal potentials to a signal processing section. In order to make use of time division on the output line in this kind of imaging device in which a plurality of pixels have a common output line, a pixel selection function is required such that only a specified pixel outputs a signal potential, and pixels other than the specified pixel do not output a signal potential. Scanning circuits to make the plurality of pixels operate sequentially, one at a time, is also required.
The above selection function problem maybe solved by providing a switch transistor at the output terminal of each pixel, but in this case all the pixels have to be provided with a switch transistor, and the requirement for an image pickup device of reduced size cannot be met. A technique to overcome this is disclosed in Japanese laid-open patent application publication number 2003-46864. In this technique the source potential supplied in common to every pixel is not fixed, but is made to vary cyclically between a high potential and a low potential. By doing this, the specified cell is made to output a signal potential exclusively without switch transistors being provided for each pixel.
Also, a scanning circuit constructed from dynamic logic is disclosed in Japanese laid open patent application publication number 2003-46879. In particular, the fact that the scanning circuit can be made to operate faster by using dynamic logic with NMOS transistors is disclosed.
However, the above solid-state image pickup device with both a scanning circuit constructed using dynamic logic and a source circuit in which in which the potential varies cyclically has the following problem.
In a scanning circuit constructed using dynamic logic, when a selected pixel outputs a signal, the potential at the output terminal goes to either one of a Hi potential or a Lo potential, the output terminals for the unselected pixels go to a high impedance, and the signal lines which tie the unselected pixels to the high impedance output terminals go into a floating state.
If the signal line goes into a floating state, the repeated transitions of the power source potential between a high potential and a low potential have an effect due to the coupling capacitance inherent in the structure of integrated circuits. Specifically, when the source potential makes a transition from a low potential to a high potential, the potential on the signal line in a floating state rises, due to the effect of the coupling capacitance, and the potential on the signal line resembles a signal to put an unselected pixel in a selected state. Hence, the signal potential from an unselected pixel is outputted, the potential on the signal line is modulated, and the signal potential from the legitimately chosen pixel can no longer be accurately detected.
Note also that the signal processing section that detects the signal potential from a pixel reads off, as the pixel signal, the size of the drop in the signal potential from a reference potential initially outputted by the pixel, this drop depending on the light intensity received by the pixel. The higher the pixel signal, the lower the potential on the output line becomes. Thus the modulating effect on the output line due to the unselected pixels cannot be ignored. This effect is known as a lowering of the dynamic range.